Refrigeration compressors emit an unacceptable level of noise. Many attempts have been made to dampen, absorb or otherwise effectively eliminate such emitted noise. None of them have been completely satisfactory for all types of compressors and applications.
In rotary compressors typically the compressor cylinder is physically attached to the side wall of the casing in order to permanently fix the position of the cylinder in the housing. A normal method of attachment is by spot welding the cylinder and casing side wall at selected positions around the circumference of the casing. During operation, the compressor repeatedly compresses charges of refrigerant gas and releases this compressed gas into the casing. The compression and release action sets up vibrations, or noise, in the compressor cylinder which tend to radiate radially outwardly toward the casing side wall.
It is believed that there are two primary paths of noise transmission. One is by the gas itself. The second is via a conduction path from the cylinder through the cylinder casing interface to the casing. It is believed that the principal mode of conduction is the second path. Of course, it is chiefly the vibration of the casing which generates the audible noise heard by consumers.
Typically the casing side wall is in very close proximity to the outer surface or wall of the cylinder. The welds attaching the cylinder and casing side wall tend to distort the side wall so that, rather than being a truly cylindrical shape, in the vicinity of the welds, the side wall extends in a generally straight line or plane between adjacent welds. This brings the side wall intermediate adjacent welds into contact with the cylinder outer wall. It is believed that such intermediate contact contributes greatly to the noise emission.